Brain Controlled Artificial Legs
R.ANJALI
-----------------------------------------------------ABSTRACT----------------------------------------------------This paper describes a brain controlled robotic leg which is designed to perform the normal operations of a
human leg. After implanting this leg in a human, the leg can be controlled with the help of user’s brain signals
alone. This leg behaves similar to a normal human leg and it can perform operation like walking, running,
climbing stairs etc. The entire system is controlled with the help of advanced microcontrollers and digital signal
processors. The signals are taken out from the human brain with the help of electroencephalography technique.
The person can perform operations like walking, running etc just by their thought. This system will be very
much suitable for those who lost their legs in accidents and the proposed system is hundred percent feasible in
the real time environment with the currently available technology.
The Brain Controlled Artificial Legs are very much cost effective when compared to the normal Artificial legs
which is available in the market. The reduction in cost of the proposed system is found to be above 80% when
compared to the existing system. Moreover, the user can have
full control over the artificial legs which is not possible in the existing system.
----------------------------------------------------------------------------------------------------------------------------- ---------Date of Submission: 01 February 2014
Date of Acceptance: 20 February 2014
----------------------------------------------------------------------------------------------------------------------------- ----------

I.

INTRODUCTION:

This paper describes a brain controlled robotic leg which is designed to perform the normal
operations of a human leg. After implanting this leg in a human, the leg can be controlled with the help of
user’s brain signals alone. This leg behaves similar to a normal human leg and it can perform operation
like walking, running, climbing stairs etc. The entire system is controlled with the help of advanced
microcontrollers and digital signal processors. The signals are taken out from the
human brain
with
the help of electroencephalography technique.The person can perform operations like walking, running etc
just by their thought. This system will be very much suitable for those who lost their legs in accidents
andthe proposed system is hundred percent feasible in the real time environment with the currently
available technology.The Brain Controlled Artificial Legs are very much cost effective when compared to
the normal Artificial legs which is available in the market. The reduction in cost of the proposed
system is found to be above 80% when compared to the existing system. Moreover, the user can have
full control over the artificial legs which is not possible in the existing system.

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Brain Controlled Artificial Legs...
A
brain-computer interface (BCI), sometimes called a direct neural interface or a brain-machine
interface, is a direct communication pathway between a human or animal brain and an external device. In this
definition, the word brain means the brain or nervous system of an organic life form rather than the mind.
Computer means any processing or computational device, from simple circuits to the complex
microprocessors and microcontrollers.An interesting question for the development of a BCI is how to handle
two learning systems:
The machine should learn to discriminate between different patterns of brain activity as accurate
as possible and the user of the BCI should learn to perform different mental tasks in order to produce
distinct brain signals. BCI research makes high demandson thesystem and software used.
Parameterextraction, pattern recognition and classification are the main tasks to be performed in a brain signals.
In this paper it is assumed that the user of this system has one leg which is functioning fully and the system is
designed accordingly. This system can be extended for both the legs and it is not limited to the basic
operation of human legs such as walking, running, climbing stairs etc. It can also perform operations like
cycling, hopping etc
Brain Waves
Electrical activity emanating from the brain is displayed in the form of brainwaves. There are four categories
of these brainwaves ranging from the most activity to the least activity. When the brain is aroused and
actively engaged in mental activities, it generates beta waves. These beta waves are of relatively low
amplitude, and are the fastest of the four different
brainwaves. The frequency of beta waves
ranges from 15 to 40 cycles a second.The next brainwave category in order
of frequency
is
Alpha. Where beta represented arousal, alpha represents non-arousal. Alpha

Fig 1: Different Types of Brain Waves
In the proposed system alpha waves and beta waves are used from the brain for signal processing. It
is assumed that the person is in alpha state and beta state (which is the case normally) and these waves are
taken out from the human brain and converted in the form of electrical signals with the help of electrode
caps. The following figure shows the different types of waves and also the mental state of the person. Those
waves usually vary from a frequency of 1Hz to 40 HZ.

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II.

GENERAL BLOCK DIAGRAM OF THE SYSTEM:

Fig2 : General Block Diagram of the Proposed System
Fig 2 shows the general block diagram of the proposed system. Electrode cap is placed in the scalp of the
person. The signals taken out from the human brain will be in the range of mV and Âľ V. Hence they are fed
to an amplifier. Then it is sent to a Analog to Digital Converter to convert the analog brain signals in to
digital form. Then it is sent to a signal processor where
parameterextraction,
pattern classificationandpattern entification are done. These digital signals are fed as input to microcontroller
unit. The last four units (Amplifier, Signal Processor, Analog to Digital Converter and Microcontroller
Unit) are placed inside the artificial leg. The output of the microcontroller unit is fed to the driving circuit.
Let us see about these blocks in detail.

III.

ELECTRODE CAP:

Fig 3 shows a person wearing an electrode cap. These electrode
caps contains electrodes which are
placed on the skull in an arrangement called 10-20 system, a placement scheme devised by the international
federation of societies of EEG. In most applications 19 electrodes are placed in the scalp. Additional
electrodes can be added to the standard set-up when a clinical or research application
demands
increased spatial resolution for a particular area of the brain. High-density arrays (typically via cap or
net) can contain up to 256 electrodes more-or-less evenly spaced around the scalp. The main function of the
electrode cap is to take the brain signals in the form of electrical signals. The signals taken out from the
Electrode cap are fed to an amplifier.

AMPLIFIER: The output signal from the electrode cap will be in the range of mV and Âľ V. So, these
signals will not be suitable for signal processing. Hence these signals are fed to an amplifier. Each electrode
is connected to one input of a differential amplifier (one amplifier per pair of electrodes); a common system
reference electrode is connected to the other input of each differential amplifier. These amplifiers amplify the
voltage between the active electrode and
the reference (typically1,000â&#x20AC;&#x201C;100,000 times, or 60â&#x20AC;&#x201C;100 dB of
voltage gain).
ANALOG TO DIGITAL CONVERTER: The output signals from the amplifier are analog
innature.
heyalso contain some unwanted signals. Hence the output signals are filtered using high pass and low
pass filters. The high-pass filter typically filters out slow artifact whereas
thelow-passfilterfiltersouthighfrequency artifacts. After the signal is filtered they cannot be directly fed to a digital signal processors and
microcontroller unit as they are in analog form. Hence these signals are sent to an Analog to Digital converter to
convert the incoming analog signals in to digital signals.
SIGNAL PROCESSOR:Using the output signal from the A/D converter, parameter extraction, pattern
classification and pattern identification are done. Then the signals are fedtoa Fast Fourier Transform Unit.
This is done to simplify the calculations. An FFT algorithm computes the result in O (N log N)
2
operations instead of O (N ) operations. The output signals from the signal processor are fed to a
Microcontroller unit.
MICROCONTROLLER UNIT: The output signals from the signal processor are fed to a microcontroller
unit. This microcontroller unit performs the robotic operation with the help of a stepper motor. It will control
the operations such as walking, running, etc depending upon the input signal. For different patterns of input
signals it will be pre-programmed to do a specific operation. The reference signal will be already stored
in the microcontroller memory in digital form. Usually
an
8
bit
or+
a
16
bit microcontroller is preferred depending upon the number of operations to be performed. The
complexity of the microcontroller programming increases with the number of operations which has to be
performed.
WORKING OF THE PROPOSED:
SYSTEM
:
For every human activity the brain waves changes its pattern. For example, if a person moves his/her hands
then a specific pattern of brain wave is obtained and if the same person moves his/her legs then a different
pattern of brain wave is obtained. Even if a person thinks of moving his/her legs a brain wave of specific
pattern is produced and it is sent to the legs and then the operation of moving the legs is performed. The
same brain

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Brain Controlled Artificial Legs...
waves are produced even for a person who is not having his/her legs. But the operation of moving the legs
will not be performed due to the absence of legs. So, just by thinking of moving the legs, a brain wave
which is capable of performing a specific operation is generated in the brain. Due to the lack of the
appropriate system, the activity will not be performed successfully.In the proposed system, the brain waves are
pre-recorded for each operation to be performed and these waves are used as reference signals. These
signals are stored in the microcontroller memory. For each reference signalin the microcontroller memory,
the robotic leg is pre- programmed to do a specific operation. When the reference signal matches with
the actual signal from the userâ&#x20AC;&#x2122;s brain, the robotic leg will do the pre-programmed operation with the
help of the microcontroller.For example, let us say that the user is thinking of walking. So a brain wave will
be produced. These waves are processed and then it is converted in to digital signals. These signals are
compared with the pre-recorded reference signals and a match in the signal pattern will be found in the
microcontroller. The operation for this particular pre-recorded signal
will be pre-rogrammed in the
microcontroller circuit i.e. walking and thus the microcontroller will send the control signal to theartificial
robotic leg and the robotic leg will perform the required operation.Usually a stepper motor controlled
robotic leg is used for this purpose. Similarly to walking, other operations can also be performed using the
artificial leg. This system is very user friendly and the system can be designed according to the userâ&#x20AC;&#x2122;s
requirements i.e. the number of operations required for the user can be fixed by him and the system can be
designed accordingly.
So the number of operations that has to be performed by the leg can be
increased or decreased and the complexity of the design varies accordingly.This idea can be extended for
both the legs and both the legs can be made to do operations like walk, run etc simultaneously. Thus the
system is versatile. This system is hundred percent feasible in the real time environment and it can
be implanted to any human irrespective of their age.
Figure 5, 6, 7, 8, 9 and 10 shows some of the pictures of artificial legs.

Fig 10: Walking with artificial legs.
POWER SUPPLY
These artificial legs are powered by a small lithium-ion battery which has to be charged once in
2 day. Lithium-ion batteries have very high charge density (i.e. a light battery will store a lot
of energy). They are of ultra-slim design and hence they occupy very less space. Moreover their life time
will be longer when compared to other batteries. Hence they are preferred when compared to other
batteries. Moreover they have longer life time when compared to other batteries.
NORMAL ARTIFICIAL LEGS:
Normal Artificial Legs, available in the market, is very costly. They use a group of sensors and a
complex algorithm for their operation which makes the existing system very costly. This disadvantage has
been overcome in the Brain Controlled Artificial Legs as they donâ&#x20AC;&#x2122;t use any sensors for their operation.
Moreover the normal artificial legs are 100% dynamic in operation. Hence the chance of occurrence of an
error is more in those systems. External appearance and output of both the legs are same. But the
method of operation is different. Hence the Brain Controlled Artificial Legs are cost effective.
Brain Controlled
Artificial Legs
[1] Ease of
[2] Construction
[3] Cost is not more than Rs.5,00,000
[4] User can have full control over the artificial leg.
Normal Artificial
Legs
1. Complex in construction
2. Cost is about
$80,000$90,000(Rs.35,00,000
to Rs.40,00,000)
3. User cannot have full control over the artificial leg.
4. Semi-Automatic
4. Fully Automatic

CONCLUSION:
Forty years ago, the technology was so basic. Newton said. “Leg sockets were made out of wood,
offering the equivalent of a door hinge at the knee”. But with the recent advancement in the technology, Brain
Controlled Artificial leg can be made as a reality. The performance of the proposed system will be better than
the existing artificial legs as the user has full control over the Brain Controlled Artificial Legs. Hence it behaves
like a normal human leg. The built-in battery lasts anywhere from 25 to 40 hours so it can support a full
day’s activity. The recharge can be performed overnight or while traveling in a car via a cigarette lighter
adapter.The cost of the proposed system is found to be very less when compared to the existing ones. So,
even the middle class people

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Brain Controlled Artificial Legs...
Who cannot purchase the existing artificial legs can make use of this proposed system. With this
systemlife can
be made easier for the handicapped persons and they can also do their day-to-day
activities normally without any difficulties.